1. Field of the Invention
This invention relates to the production of halogenated butyl rubber and more particularly to a halogenated butyl rubber containing combined bromine and chlorine in the polymer molecule. More particularly, the present invention relates to a novel, continuous and efficient process for reacting isobutylene-isoprene butyl rubber with gaseous bromine chloride to form a bromochlorinated product.
Chlorinated butyl rubber and brominated butyl rubber are each well known in the art, as well as the butyl rubber from which they are derived. Prior art techniques for producing halogenated butyl rubber containing both bromine and chlorine were inefficient processes which required either sequential halogenation with one halogen at a time or the use of laminar flow conditions and liquid bromine chloride, which is undesirable compared to the use of bromine chloride vapor.
2. Prior Art
Halogenated butyl rubber, as represented by chlorinated butyl rubber and brominated butyl rubber are well known in the art and are commercially available products. Numerous patents related to these products are available, but only those dealing with butyl rubber containing both chlorine and bromine prepared by the use of bromine chloride are relevant to the instant application. Additional references are available which either incidentally disclose bromine chloride in a list of potential halogenating agents for butyl rubber, see e.g., U.S. Pat. No. 3,018,275 to D. L. Cottle, at col. 2, line 45, or teach methods for preparing a halogenated butyl containing both chlorine and bromine by starting with, e.g., a chlorinated butyl rubber and brominating it, or e.g., vice versa, e.g., see U.S. Pat. No. 3,009,904 to G. E. Serniuk, et al, especially col. 2, lines 15-22. The latter reference also suggests, at col. 2, lines 5-11, that mixed halogens can be introduced into butyl rubber by reacting it with a mixture of bromine and chlorine. However, no process is disclosed for accomplishing this purpose and no direction is given to utilize bromine chloride in the vapor form as the preferred reagent. Additionally, the several techniques for producing a polymer containing both bromine and chlorine are suggested as equivalent, alternative methods for providing the same product. Clearly, there was no recognition of the unique product achievable by the process disclosed herein.
The reaction of bromine chloride with butyl rubber is described in U.S. Pat. No. 3,966,692, issued June 29, 1976 to R. F. Driscoll, et al, e.g., Example II therein discloses the reaction of bromine monochloride with butyl rubber in a hexane solution. However, this reference specifically requires laminar flow of the reacting streams (e.g. col. 1, lines 50-51) and the preferred use of liquid bromine chloride (e.g., col. 2, the paragraph starting at line 26) and, as an essential feature, maintenance of positive pressure on the reacting system to prevent volatilization of the organic solvent, halogen or halogen halide (col. 3, lines 21-30).
The use of bromine chloride to halogenate polybutadiene or butadiene-isoprene copolymers is disclosed in British Pat. No. 1,483,063 and the similar halogenation of polyisoprene is disclosed in British Pat. No. 1,483,064. Both patents are limited to the specific polymers cited with no indication that halogenation would be successful with other polymers, especially one of substantially lower unsaturation, e.g., butyl rubber. In addition, both patents are directed to producing polymers containing at least 55% halogen with at least one chlorine atom and at least one bromine atom for each two monomer units in the British Pat. No. 1,483,063 patent and two chlorine atoms and at least one bromine atom for each two monomer units in the British Pat. No. 1,483,064 patent. The bromine to chlorine molar ratios differ markedly from those achieved in the instant invention. Process features to achieve the desired product also differ substantially, see e.g., the British Pat. No. 1,483,064 patent at lines 85-87 wherein a preferred molar ratio of bromine chloride to polyisoprene of 6:1 is disclosed.
The preparation of bromochlorinated butyl rubber was referred to in U.S. Pat. No. 4,130,519 to Roper, et al (col. 4, starting at line 10), issued Dec. 19, 1978. That general disclosure is based on the invention disclosed herein, the assignee of the entire interest in both cases being the same and two of the inventors in each case also being the same.